Microfabrication techniques originally developed for the semiconductor industry afford the opportunity to design microarray devices that, when used in conjunction with living cells as chemosensors, allow analyte detection that is extremely sensitive and can be highly automated. Furthermore, the devices can be mass produced at low cost.
Living cells are perfect chemosensors due to their exquisite sensitivity to a variety of complex chemical compounds. Ligand binding to G-protein coupled receptors (GPCR) activates enzymatic cascades that amplify the signal, enabling cells to respond to minute quantities of ligand. These cascades also direct the stimulus to a specific cellular response. In insects, for example, pheromone, odorant and taste receptive GPCRs activate phospholipase C (PLC), which releases inositol 1,4,5-triphosphate (IP3) and diacylglycerol through hydrolysis of phosphatidyl inositol 4,5 bisphosphate. IP3 production in turn releases Ca+2 from intracellular stores, instigating a rise that then triggers a variety of cellular responses, including the stimulation of cellular secretion through exocytosis.
As another example, endocrine cells and nerve cells secrete hormone and neurotransmitter, respectively, by a regulated secretory pathway in which an increase in intracellular Ca++ concentration triggers the fusion of hormone-containing membrane vesicles with the plasma membrane releasing hormone.